If a closed window lets in a noticeable draught, the cause is almost always one of three: a worn seal, an unadjusted sash or failed installation joints. Each has its own signs — and its own fix.
1. A worn seal
The seal is what makes a window airtight. After 5–10 years the rubber loses elasticity, cracks and no longer presses against the frame. Signs: cold is felt around the whole sash perimeter, the rubber is hard, flattened or visibly cracked.
Quick test: close the window on a sheet of paper. If you can pull the sheet out without resistance, the seal is not working at that point.
The fix — seal replacement. For a PVC window it costs from €40 per sash and takes 20–40 minutes.
2. An unadjusted sash
Over time the sash sags and no longer presses evenly against the frame. Cold is then felt in one specific spot — usually a top or bottom corner. Hardware also has a winter/summer mode: the cams can be turned for stronger compression in winter.
The fix — adjustment (from €15). A technician sets the hinges and compression cams around the whole perimeter.
3. Installation joints and the sill
If the draught comes not from the sash but along the frame edge, from under the sill or around the reveal — the problem is the installation joint. Foam shrinks over time, especially if the joint was not protected from moisture and UV.
The fix — joint sealing or insulation (from €80). The exact leak can be located with a thermal camera.
What not to do
- Do not stick adhesive tapes onto the seal — they interfere with the hardware and damage the rubber.
- Do not fill gaps with silicone — the sash must stay openable.
- Do not force the handle — it deforms the hardware.
Conclusion: A draught is not something to live with, nor a reason to replace the window. Seal replacement, adjustment or joint sealing solves it for a fraction of the cost of a new window — and heating bills drop from the very next month.